Prior art trenching machines for trenching pipelines are known to have serious drawbacks. Some trenchers, for example, are self-propelled on hydraulically driven wheels which ride on the coating of the pipeline. These wheels are hydraulically pressed against the surface of the pipe for the purpose of not only developing sufficient traction to move the trenching machine, but also for the purpose of riding over surface obstacles in the pipeline itself, such as anodes or merely riding over areas of varying diameter.
It is also commonly known that trenching machines must work in a wide range of soil conditions from extremely soft sand to hard clay and the like. The cutting requirements are thus similarly broad. And in case of elongate nozzle assemblies, vertically oriented on the trenching machine, it has been found that substantial pressure drops through the length of the cutting nozzles produces a diminished cutting action from one end of the cutting assembly toward the low pressure end, thus resulting in an inconsistent cutting action in which one end of the cutting assembly is more effective than the other end due to the pressure drop through the length of the nozzle assembly.
Due to the necessity to drive the trenching machine over the surface of the pipeline, and simultaneously produce sufficient cutting action by the nozzles or other cutters, substantial power requirements are necessary. Since, as indicated above, the trenching machines must work in hard, as well as soft soils, the necessary power requirement at any given time may be substantially greater than required. Thus, the prime movers of known trenching machines are provided with complex control mechanisms that are characterized by gears, clutches and control knobs for the purpose of preventing the cutters from stalling and enabling adjustment of the power to the cutter assemblies. Among the consequences of these substantial energy requirements are the necessity for carrying large diesel engines on the floating vessel accompanying the trenching machines, greater energy requirements for operating the trencher, and relative inefficiency in operation of the trenching machine on a basis of cost per unit of foot trenched.